1. Technical Field
The present invention relates in general to cooling systems for electronic systems and, in particular, to the monitoring of the operation of cooling apparatus. More particularly, the present invention relates to a multiple fan monitoring circuit and method of operation thereof for monitoring a number of cooling fans utilizing a single sense input.
2. Description of the Related Art
Integrated circuits and other electrical devices generally have rated operating temperature ranges. Within these operating ranges, the devices behave according to specified requirements. Outside of the rated operating range, the response characteristics of the circuits and devices can vary from the specified requirements. At elevated temperatures, it is known for integrated circuits and other electrical devices to fail or burn out or otherwise become defective. Accordingly, it is desirable to maintain circuits and devices within their rated operating temperature ranges.
In a computer system, continued operation of an electronic device leads to the generation of heat. In some instances, albeit rare, ambient air is sufficient to provide cooling to maintain the circuit or device within the desired operating temperature range. However, some circuits or components generate enough heat to require affirmative cooling from a cooling fan. Typically, computers have included a cooling fan inside the computer housing to prevent overheating caused by the normal operation of the computer. Also, it not uncommon for a computer system, such as a server system, to utilize more than one cooling fan to maintain a specified operating temperature.
Computer systems must monitor their cooling fans to verify that the fans are powered on and rotating at a predetermined speed to maintain a desired thermal condition that precludes accelerated failures of electronic devices utilized in the computer systems. Typically, each cooling fan generates a xe2x80x9cfeedbackxe2x80x9d signal that provides information, such as rotational speed. A monitoring processor, typically a system processor, receives this feedback signal at a fan sense pin. As additional fans are added to a system. e.g., to compensate for additional electronic devices due to system upgrades, the number of fans may exceed the number of fan sense pins available for monitoring the fans"" status.
Accordingly, what is needed in the art is an improved method for monitoring cooling fans that mitigates the limitations discussed above. More particularly, what is needed in the art is a means for monitoring the operational status of more than one cooling fan utilizing a single sense pin.
It is therefore an object of the invention to provide an improved data processing system.
It is another object of the invention to provide a multiple fan monitoring circuit for monitoring a plurality of fans utilizing a single sense input.
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a multiple fan monitoring circuit for use with a plurality of fans, wherein each of the fans operates at a different frequency and generates a tach signal indicative of the fan operation is disclosed. The multiple fan monitoring circuit includes a number of waveform shaping networks, wherein each of the waveform shaping networks is coupled to a corresponding one of the fans. Each of the waveform shaping circuit is utilized to waveshape a tach signal generated by its corresponding fan. The multiple fan monitoring circuit also includes a frequency processing circuit, coupled to the waveform shaping networks, that receives the waveshaped tach signals at a single sense node. In a related embodiment, the frequency processing circuit includes a summing circuit, coupled to the single sense node, that combines the waveshaped tach signals into a single combined signal. The frequency processing circuit also includes a frequency discriminator, coupled to the summing circuit, that separates the single combined signal into multiple components, wherein each of the multiple components corresponds to a particular fan.
The present invention recognizes that as additional fans are added to a system, the number of fan sense pins available for monitoring fan status and operation becomes a limiting factor. Typically, a system architecture only provides a limited number of fan sense lines. As soon as the number of fans employed in the system exceed the number the number of fan sense lines, the system cannot monitor and ensure that all the fans are operational, e.g., powered on and rotating at the appropriate speed, to maintain a desired thermal condition. The present invention overcomes the problem of limited fan sense lines by disclosing a novel multiple fan monitoring circuit that allows a single sense line to monitor more than one fan.
In another embodiment of the present invention, the frequency processing circuit further includes an analog to digital converter to convert the single combined signal from an analog signal to a digital signal. In an advantageous embodiment, a fast fourier transform (FFT) process is then utilized to separate the single combined signal into multiple components, each of which corresponds to a different fan.
The foregoing description has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject matter of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.